Two joint buyers expressed interest in purchasing a coal-fired power plant on the Navajo Nation. This news came as Gov. Doug Ducey signed legislation that would exempt coal used at the plant from the state's sales tax.

Avenue Capital Group, a New York hedge fund, and Middle River Power, a Chicago private equity group, have been in discussions with one of the utilities that operates the Navajo Generating Station about buying the plant. The utility said in an email the buyers may have missed the contractual deadline.

Ducey called the tax break "essential for the Navajo Nation, the Hopi Tribe and surrounding communities" to protect the 800 rural jobs at the power plant and mine.

The Institute for Energy Economics and Financial Analysis, an Ohio-based research group, has listed "six insurmountable business risks" to keeping the plant open. They included the competition from cheaper natural gas and renewable energy and the cost of retrofitting an aging plant to comply with environmental regulations.